Known silver halide color photographic elements include those having coupler compounds incorporated therein which, when subjected to the color development, react with an aromatic primary amine type color developing agent which has been oxidized by the development of exposed silver halide to produce dyes, such as indophenol, indoaniline, indamine, azomethine, phenoxazine, phenazine and like dyes, and form colored images.
Therein, it is necessary to convert only the coupler which is incorporated in the same layer as light-sensitive silver halide, and more particularly, the coupler present in the vicinity of optically exposed silver halide into the corresponding dye in the color development process. In practice, however, this requirement frequently cannot be fully satisfied, and a phenomenon referred to as color fog or color contamination frequently occurs.
As one category of color fog, there is the phenomenon called airial fog, in which a developing agent is oxidized by air to some extent, and the resulting oxidized portion of developing agent reacts with couplers to form dyes at such places in the photographic material that any silver images are not formed.
As another example of color fog, mention may be made of a phenomenon in which there occurs the generation of stain or desensitization in a sensitive material having at least one coupler-containing silver halide hydrophilic colloidal layer provided on a hydrophobic support whose surface has just been exposed to electron beams, as described in U.S. Pat. No. 3,582,333.
Furthermore, the color mixing phenomenon becomes a problem in some multilayer color photographic elements in which plural emulsions differing in color sensitivity are coated in multiple layers on the same support. In order to obtain images having excellent color reproducibility in sensitive materials having multilayered structures, it is essential that only the coupler incorporated in the same layer as optically exposed silver halide develop a color.
However, a phenomenon also occurs which is called color mixing, in which oxidized aromatic primary amine type color developing agent which is produced in the step of color development does not remain only in the layer where it was produced, but some portion thereof diffuses into adjacent layers because of its low molecular weight, and, at the same time, oxidized developing agent from other layers diffuses into this same layer through the adjacent layers, resulting in a lack of correspondence of color sensitivity with color development. For instance, in the case of a negative type sensitive material is exposed to green light, natural color development ought to result solely in magenta-coloration, but, in practice, cyan- and yellow-colorations also occur. Furthermore, although these colorations occur to small extent, color reproducibility is lowered.
In general, the addition of a reducing substance to an interlayer, the uppermost layer, or the lowermost layer of coupler-containing silver halide photographic material, as described in U.S. Pat. Nos. 3,960,570, 3,700,453 and 3,582,333 has been employed for the purpose of the prevention of color mixing, color fog, and color stain. The reducing substances which have generally been employed for the above-described purpose are hydroquinone derivatives, with specific examples including those described in the foregoing U.S. Patents and U.S. Pat. Nos. 2,360,290, 2,403,721, 2,418,613, 2,701,197, 2,710,801, 2,735,765, 2,732,300, 2,704,713 and 3,700,453 and so on. However, as is noted in U.S. Pat. No. 3,960,570, it is known that a monoalkylhydroquinone having an alkyl moiety containing less than 9 carbon atoms diffuses through hydrophilic colloidal layers in the presence of a developing solution, that is, in the alkaline environment in which the hydroquinone compound is expected to have an effect on the prevention of color mixing and stain. Thus, such monoalkylhydroquinones do not stay in the intended layer and thus the intended result cannot be fully obtained and there is a possibility of undesirable adverse effects, to make matters worse. Methods which have been developed for preventing the above-described disadvantage are described in U.S. Pat. Nos. 2,360,290, 2,728,659 and 3,700,453.
According to the method described in U.S. Pat. No. 2,728,659, a hydroquinone derivative which is substituted with an alkyl group and slightly soluble to water is added to the intended layer in the form of dispersion, which is prepared by dissolving it in a high boiling point organic solvent which is also slightly soluble to water, such as dibutyl phthalate or tricresyl phosphate, and then dispersing the resulting solution into a hydrophilic colloidal medium in a state of fine droplets. One of the problems of this method is the low solubility of the hydroquinones substituted with alkyl groups in high boiling point solvents, as a consequence of which crystals separate out in the layer to which the dispersion is added. Another problem thereof is that an extra step is required for emulsifying and dispersing the hydroquinone compounds in a proper medium. Further, the specification of U.S. Pat. No. 3,700,453 describes that when di-t-octylhydroquinone or di-n-dodecylhydroquinone as described in U.S. Pat. No. 2,360,290 and 2,728,659 is used as the hydroquinone derivative, a large portion of the hydroquinone derivative separates out in a form of crystal even when tricresyl phosphate is employed in a proportion of 0.5 part to 1 part of the hydroquinone derivative, that is to say, it is practically impossible to use such hydroquinone derivatives for the above-described purpose. Furthermore, U.S. Pat. No. 3,700,453 describes a method for overcoming the above-described disadvantage in which two or more of hydroquinone derivatives substituted with secondary alkyl groups containing more than 9 carbon atoms are used in combination, and also describes a method for obtaining such mixtures in which hydroquinone and primary olefins having more than 9 carbon atoms are allowed to react with one another in the presence of a Lewis acid catalyst at a high temperature for an extended period of time, and the resulting reaction mixture is obtained therefrom by distillation. Although this method is considered to be a useful technique for obtaining stable emulsified dispersion, it is also supposed to suffer from the defect that it is difficult to stabilize the quality of the product so that the composition ratio of the components of the mixture is kept constant. Particularly, it is reported in Example 1 of the above-described patent that dodecylhydroquinone prepared by the reaction of hydroquinone with 1-dodecene was confirmed by chromatography to be the mixture of five kinds of monoalkyl substituted hydroquinones and twelve kinds of dialkyl substituted hydroquinones, and therefore it is thought to be nearly impossible for the composition ratios to be kept constant.
The above-described method suffers from another defect in that the efficiency per unit weight is low, which is believed to result from the small proportion of the photographically active hydroquinone moiety with respect to the alkyl substituent moiety.
In order to remove these defects regarding nondiffusibility and the stability of emulsified dispersion, diffusion-resistant hydroquinone polymers have been developed, as described in U.S. Pat. No. 2,816,028. However, the introduction of hydrophilic groups is required for introducing hydroquinone moieties into a polymer and consequently, the proportion of hydroquinone moiety in the polymer per unit weight is decreased.